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Reports of research work funded by grants prior to 2015

University of Otago Wellington

Is the Rising Popularity of Long-Acting Contraception Impacting on Chlamydia Rates?

SB Rose, S Garrett, S Pullon, T Stanley
Department of Primary Health Care and General Practice


New Zealand has high rates of sexually transmitted infections (STIs), unplanned pregnancy, teenage pregnancy and abortion when compared to other developed countries, with younger women disproportionately affected by these issues.  Unintended pregnancy and STIs have significant personal and public health costs, and although rates of teen pregnancy and abortion have been slowly declining in recent years, both unintended pregnancy and STI rates remain high.  The reasons for declining rates of unintended pregnancy are not clear, but the role of long-acting reversible contraception (including intrauterine devices and subdermal implants), commonly referred to as ‘LARC’ might be a key factor.

LARC use has reportedly increased in recent years due to better access (including government funding) and an increasing awareness of their effectiveness in preventing unintended pregnancy. Despite providing the highest level of protection against pregnancy, LARC methods provide no protection against STIs.  Condoms used consistently and correctly provide the most effective protection against transmission of STIs.  Dual method use (LARC and condoms) is therefore required to protect against unintended pregnancy and STIs.

The increasing use of LARC in New Zealand has anecdotally been linked with concerns about declining use of condoms and increasing rates of STIs such as Chlamydia.  Chlamydia is the most commonly diagnosed STI in New Zealand, with highest rates among females aged 15-19 years and males aged 20-24 years.  If undiagnosed and untreated, Chlamydia can have serious short and long-term health consequences including pelvic inflammatory disease and infertility.  There is no screening programme for Chlamydia in New Zealand, and up to 80% of infected females will be asymptomatic.  Detection of Chlamydia is typically reliant on opportunistic screening that often occurs during a consult related to contraception or a cervical smear.  LARCs are effective for 3-5 years, negating the need for regular health consultations associated with other commonly used contraceptives, potentially resulting in fewer opportunities for STI screening and reminders about condom use for STI prevention.


To determine whether women initiating LARC methods have differential rates of Chlamydia testing and diagnosis than non-LARC users.


Design:  Retrospective cohort study

Data collection:  Data pertaining to a large cohort of women discharged from the CCDHB abortion clinic between 2009 and 2012 (of whom approximately half received a LARC insertion prior to discharge), were linked via NHI number to laboratory data to identify testing and detection of Chlamydia in the two years following LARC initiation.  Hospital clinic data included: date of abortion, age, ethnicity, NZDep, parity, pregnancy history, type of procedure (surgical/medical).  

Type of long-acting contraceptive method initiated post-abortion (IUD or implant) was collected from patient notes in a previous study, but data on short-acting (non-LARC) method choice was collected as part of the current study.  Laboratory data collection included all Chlamydia test episodes recorded against NHIs for the study cohort between Jan-2009 and Dec-2014.


This study commenced in January 2015 (with receipt of salary-funding from a University of Otago grant) and is currently ongoing.  The study is due for completion on 31 December 2015.

Data collation and preparation for analysis

  • Lab data received: February 2015 (23,690 records)
  • Contraceptive data collection at hospital clinic: February-May 2015 (4037 records reviewed, data entered and checked for accuracy)
  • Extensive cleaning and collation process of hospital and lab datasets: February 2015 – present (including: identification of missing data in hospital dataset, request patient notes to retrieve missing data, identification of multiple visits during follow-up period, removal of duplicate specimens tested on the same day in lab dataset, identification of Chlamydia test performed at the time of contraceptive method initiation, ordering of test data by date, transposing multiple lines of data into a single record for 6222 individuals, combining hospital and lab data into one dataset; recoding variables in preparation for analysis).
  • Final checking and preparation for analysis: Due for completion end July 2015


Data analysis is due to commence August 2015. Outcome measures:

  1. Proportion of LARC and non-LARC users tested for Chlamydia in the 24 months following contraceptive method initiation (reported by age, ethnicity, parity, NZDep, previous Chlamydia).
  2. Proportion of LARC and non-LARC users testing positive for Chlamydia in the 24 months following contraceptive method initiation (reported by age, ethnicity, parity, NZDep, previous Chlamydia).
  3. Hazard ratios (and 95% confidence intervals) for Chlamydia testing and detection following LARC initiation and adjusting for likely confounders (age, ethnicity, parity, NZDep, previous Chlamydia).
  4. Time from contraceptive method initiation to subsequent chlamydia test (survival analyses).


To our knowledge this study will be among the first to address the question of whether the rising popularity of LARC use for the prevention of unintended pregnancy is occurring at the expense of STI prevention.  Optimising prevention of both unintended pregnancy and sexually transmitted infections is an important public health challenge.  While access to, and use of LARC methods is important for pregnancy prevention, steps need to be taken to ensure women and their partners also protect themselves against the transmission of STIs (including consistent condom use).  Younger age, Maori and Pacific ethnicity are known risk factors for Chlamydia.  Identifying other independent risks (such as LARC use) would assist clinicians in the provision of screening and health promotion messages. The results of this study will potentially inform the implementation of practical interventions designed to ensure women and their partners are equipped to protect themselves against both unwanted pregnancy and STIs.

Is the Rising Popularity of Long-Acting Contraception Impacting on Chlamydia Rates?

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